Identifying
Rust Diseases
of Wheat and Barley
Rust diseases are among the most widespread
and economically important diseases of cereal crops
worldwide. Three distinct diseases, leaf rust, stripe
rust and stem rust, occur on wheat and barley in
North America. The fungi that cause these diseases
are notorious for their ability to increase rapidly and
overcome the resistance of wheat or barley varieties.
The potential yield loss caused by these diseases
depends on host susceptibility and weather conditions,
but the loss also is influenced by the timing and severity
of disease outbreaks relative to crop growth stage. The
greatest yield losses occur when one or more of these
diseases occur before the heading stage of development.
Early detection and proper identification are critical
to in-season disease management and future variety
selection.
Emerging Races of Stem Rust
Stem
Figure 1. The diagnosis of rust diseases
requires some basic understanding of
plant anatomy and a quick review of this
information may improve the accuracy of the
identification process.
Leaf
sheath
Historically, stem rust has been an extremely
important disease of wheat and barley. A series
of severe outbreaks occurred in North America
between 1900 and the 1950s, affecting grain
production in the Great Plains, many Midwestern
states, and Canada. More localized outbreaks of
the disease occurred in the southern Great Plains
as recently as 1985-1986. In all of these cases, the
increased frequency and intensity of the stem rust
epidemics was associated with the emergence of
new races of the fungus that were able to overcome
the genetic resistance of many popular varieties.
Once again, after several decades of control
with disease-resistant varieties, new races of the
stem rust fungus are threatening grain production in some parts of the world. The first of these
variants, known as “Ug99,” was initially reported
in the East African countries of Uganda,
Kenya, and Ethiopia. Additional variants also have emerged, further
complicating efforts to contain the
problem. The disease continues
to spread and may soon threaten
Leaf wheat and barley production
blade in North America. The rapid
detection of the new races is
an important component of the
international response to these
emerging disease threats.
Stem rust
Leaf rust
Parts of plant infected: Commonly affects stems,
leaf sheaths, and leaf blades; occasionally will affect
parts of the head
Shape and distribution of lesions: Oval-shaped
or elongated blister-like lesions scattered on
affected tissues, lesions visible on both sides of leaf
Lesion color: Orange-red
Degree of damage: Tearing of outer layers of
plant tissue that is visible without magnification
Parts of plant infected: Commonly occurs on
leaf blades, but may also affect leaf sheaths; infections of stems and heads are rare
Shape and distribution of lesions: Round or
slightly elongated blister-like lesions scattered on
affected tissues
Lesion color: Brown
Degree of damage: Tearing of outer layers of
plant tissue rare, visible with magnification
Stripe rust
Parts of plant infected: Commonly affects leaf
blades, occasionally observed on heads when
disease is very severe; infection of leaf sheaths or
stems is rare
Shape and distribution of lesions: Small, round,
blister-like lesions that merge to form stripes
Lesion color: Yellow-orange
Degree of damage: No tearing of outer layers of
plant tissue
Identification of Rust Diseases
Differentiating the rust diseases can be difficult, but with
practice they can be reliably identified. Begin by considering
broad characteristics such as which plant parts are affected
(Figure 1) or arrangement of the blister-like lesions on plants.
These characteristics will often separate one or more of these
diseases quickly. Continue by examining less obvious characteristics including lesion size, shape, and color to either confirm
the diagnosis or separate the more similar diseases. For example,
stripe rust is the only one of these diseases to have the blisterlike lesions organized into stripes on the leaves (left). If the
lesions are scattered on the affected plant parts, both stem rust
and leaf rust are a possibility and additional characteristics must
be considered. Leaf rust typically causes small, round lesions on
the leaf blades and leaf sheaths. In comparison, stem rust causes
oval or elongated lesions and is capable of infecting nearly all
aboveground parts of the plant, most notably the true stems
(Figure 2).
Leaf rust
Stem rust
Figure 2. Comparison of the stem rust and leaf rust lesions on
leaf tissue. Note the larger diamond shape of the stem rust relative
to leaf rust.
All three diseases have unique interactions with common
varieties of wheat and barley. These interactions can modify
the disease symptoms resulting in reduced lesion size and
varying amounts of yellow or tan tissue surrounding the
lesions (Figure 3). Becoming familiar with the range of
possible symptoms for these diseases will improve the
accuracy of the diagnosis and the management of these
economically important diseases.
Leaf rust
Figure 3. Examples of the variability in symptoms caused
by stem rust (below), leaf rust (upper right) and stripe rust
(lower right) as a result of unique interactions with wheat
or barley varieties.
Stem rust
Stripe rust
Acknowledgements
This publication was developed by the multi-state
extension and research committees for small grain diseases,
NCERA-184 & WERA-97. Publication authors:
Erick De Wolf, Kansas State University; Tim Murray,
Washington State University; Pierce Paul, The Ohio State
University; Larry Osborne, South Dakota State University;
and Albert Tenuta, Ontario Ministry of Agriculture,
Food and Rural Affairs. Photo credits: Erick De Wolf,
Robert Bowden, William Bockus, and Mary Burrows.
Development and distribution of the publication sponsored by the USDA-CREES Extension Integrated Pest
Management program award 2009-41533-05331.
This publication was developed and distributed with the assistance of the U.S. Department of Agriculture (USDA). The USDA prohibits discrimination in all its programs and activities on the basis
of race, color, national origin, age, disability, and where applicable, sex, marital status, familial
status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal,
or because all or part of an individual’s income is derived from any public assistance program.
January 2010
For additional assistance identifying
diseases of wheat or barley contact:
Jan Byrne, Plant Pathologist
Michigan State University Diagnostic Services
101 Center for Integrated Plant Systems
East Lansing, MI 48824-1311
(517) 355-4536
[email protected]
www.pestid.msu.edu